Epoxy resins have been widely used as adhesives, sealants and coating compositions in the fields of civil engineering, architecture, electronic equipment and the like in view of their favorable properties including the excellent adhesion and strength.
Epoxy resins are highly reactive, and when an epoxy resin is mixed with an amine component, it easily reacts with the amine component to cure. Therefore, most epoxy resins have been used in two-part form.
Under such situation, various attempts have been made to develop one-part resin compositions by using a ketimine compound or the like as a latent curing agent. However, no system have been so far been developed that exhibits well balanced shelf stability and curability.
For example, JP-A 5-132541 discloses a technique wherein reactivity during the storage is reduced by using a long chain polyoxylene for the skeleton of the ketimine compound to thereby improve shelf stability. This resin, however, slowly cures when it is taken out of the container and is not a one-part epoxy resin composition of practical level.
In addition, the resin compositions comprising an epoxy resin and a ketimine compound also suffer from the drawback of poor flexibility of the cured product.
On the other hand, organosilicon compounds having ketimine structure are known, and various process of their synthesis and various techniques of their use as a tackifier or a curing agent to be blended in the resin composition are also known. Number of the ketimine group in the molecule of such known compounds are one or two, and in most cases one.
The ketimine compound are synthesized, for example, by a process wherein an alkoxysilane having amino group is reacted with a ketone in the presence of anhydrous sulfate or a molecular sieve (see JP-A 3-263421 and JP-A 7-247295), a process wherein an alkoxysilane having amino group is gradually introduced into a ketone by heating (see JP-A 7-247294), or a process wherein an organic unsaturated compound having ketimine group is reacted with hydroalkoxysilane in the presence of a transition metal catalyst (see JP-A 4-83439). Many of the processes for synthesizing organosilicon compound having ketimine structure attempts to obtain the product in monomer form by suppressing the side reaction, namely, polymerization of the alkoxysilane moiety, for example, by using a dehydrating agent which removes the water generated by the reaction between the amine and the ketone.
There is also disclosed a process wherein a compound having secondary amino group in the molecular skeleton is reacted with an alkoxysilane having a halogen atom to produce a silane coupling agent having two ketimine group in the molecule (see JP-A 8-27167).
With regard to the techniques wherein an organosilane compound having ketimine structure is used as a component to be blended in a composition, there are disclosed a technique wherein an organosilane compound having ketimine structure is used as an additive for imparting adhesive properties and heat resistance to the one-part chloroprene-based adhesive (JP-A 8-27447), a technique wherein an organosilane compound having ketimine structure is used as a curing agent for hot melt epoxy resin which is solid at room temperature (JP-B 57-11582), a technique wherein a β-dicarbonyl compound is reacted with a silane coupling agent with stirring at room temperature for use as a tackifier for a polyurethane or a modified silicone (JP-B 2-19866).
The organosilane compounds having ketimine structure in the disclosed techniques, however, all suffered from insufficient shelf stability and, for example, experienced viscosity increase or gelation with lapse of time when the organosilane compound was mixed with an epoxy resin or a polyurethane resin and stored in sealed condition since nitrogen atom in the imine moiety had high nucleophilicity. Conventional organosilane compounds having ketimine group which have been used as a curing agent for an epoxy resin have been mostly bifunctional, and such bifunctional organosilane compounds have suffered from insufficient shelf stability, and the situation has been worse in the case of multifunctional organosilane compounds having ketimine group.
A plurality of inventions attempting to improve the shelf stability of the one-part, room temperature moisture curable resin compositions have been disclosed. The shelf stability in these inventions, however, have all been improved in the sacrifice of the reactivity itself, and the one-part, room temperature moisture curable resin compositions of such inventions have been far from being practical. For example, a composition prepared by mixing an epoxy resin having an increased molecular weight and a long chain polyether for the skeleton with a ketimine compound is disclosed (See JP-A 5-230182). This composition, however, does not have a curing speed adapted for use in a one-part, epoxy resin composition.
A technology wherein a sterically hindered compound wherein an amine or a thiol is capped with a trialkylsilyl group is used for a latent curing agent is also disclosed (JP-A 1-138221, JP-A 2-36220). This curing agent sensitively reacts with a minute amount of moisture, and undergoes gelation during its storage by contact with a minute amount of moisture.
In addition, epoxy resins have the drawback of low wet surface adhesion in spite of its strong adhesion to a wide variety of materials. In view of such situation, improvement of the wet surface adhesion has been attempted by using a polyamine or a polyamideamine curing agent. Such conventional known attempts have so far failed to develop one-part adhesive because of the insufficient shelf stability.
Improvements in the wet surface adhesion by using a silane coupling agent has been also proposed. The one-part epoxy resin compositions which have so far been proposed have confronted with the difficulty in balancing the shelf stability and the curing rate.
In the meanwhile, one-part curable resin compositions of modified silicone series have suffered from insufficient adhesion to concretes and mortars, and required simultaneous use of an epoxy resin and a latent curing agent for an epoxy resin.
One-part sealants employing the one-part curable resin compositions of modified silicone series have used tin compounds for the curing catalyst, and such sealants have been highly reactive and sensitive to moisture. Therefore, a dehydrating agent such as vinylsilane had to be blended in such sealants to thereby remove the water of a minute amount in the system and maintain the shelf stability. Although the shelf stability has been improved by such means to some extent, the curing rate of the sealant once it is taken out of the container are yet to be improved, and there is a demand for a latent curing agent with better shelf stability. Because of the difficulty in balancing the shelf stability and the curing rate, a one-part sealant adapted for an industrial scale production which is excellent in both the shelf stability and the curing rate has not been so far developed.
In view of such situation, an object of the present invention is to provide a one-part, room temperature moisture curable resin composition which exhibits good shelf stability and fast curing rate once taken out of the container, and which may further exhibit flexibility; a one-part, room temperature moisture curable resin composition which exhibits good shelf stability and curability as well as wet surface adhesion or initial thixotropic properties; a silicon containing compound having ketimine group whose reaction with the epoxy resin during the storage is prevented by the presence of a bulky alkyl group near the ketimine group and which exhibits good shelf stability and curability, and its production method; a one-part, room temperature moisture curable resin composition containing said silicon containing compound adapted as a latent curing agent which exhibits good shelf stability and short, curing period once taken out of the container; and a novel method of ketimine synthesis.